This invention relates generally to battery power supply and, more particularly, to thermal management in such battery power supply systems. The word “battery” here is meant to include various forms of electrochemical power generation which have in common that chemical energy, in the form of one or more chemical reactants stored in a confined space, react with each other or with an external reactant in an electrochemical reaction, so as to produce electric power when desired.
Various uses of battery power supplies have been well established. For example, the packaging together of a plurality of cells in a parallel or series configuration to form a battery module or pack for use as a power supply for personal electronic devices such as cell phones, lap top computers, camcorders or the like have become well-known and common. In addition, desirable properties or characteristics of battery power supplies including, for example, the capability of certain battery power supplies to be recharged makes such battery power supplies an attractive potential power source for vehicle propulsion, i.e., electric vehicles (EV). Recently, the concept as well as the application of battery power have been extended to include “fuel batteries” or “fuel cell batteries”, in which a fuel cell reaction is used to generate electric power in a manner somewhat similar to that of a conventional rechargeable battery, but in which one of the reactants (the fuel) must be replenished from time to time.
In various such applications, it is common that a number of cells are packed together in a preselected configuration (e.g., in parallel or in series) to form a battery module. A number of such battery modules may, in turn, be combined or joined to form various battery packs such as are known in the art. During operation and discharge, such cells, battery modules, or battery packs commonly produce or generate quantities of heat which can significantly detrimentally impact the performance that results therefrom. Thus, in order to maintain desired or optimal performance by such cells or resulting battery modules or battery packs, it is generally important to maintain the temperature of such cells, battery modules or battery packs within fairly narrow prescribed ranges.
In practice, temperature variations between individual cells can result from one or more of a variety of different factors including, for example:
1) changes in ambient temperature;
2) unequal impedance distribution among cells; and/or
3) differences in heat transfer efficiencies among cells.
Differences in heat transfer efficiencies among cells can typically be primarily attributed to the cell pack configuration. For example, cell elements at the center of a module or cell pack configuration may tend to accumulate heat while those cell elements at the periphery of the module or cell pack configuration will generally tend to be more easily or freely cooled as a result of greater relative heat transfer to the surrounding environment. Further, such variation in heat transfer efficiencies may lead to further differences in impedance such as may serve to amplify capacity differences among the cells. Such capacity imbalances can cause or result in some cells being over-charged or over-discharged which in turn may result in premature failure of a specific cell element or of an associated cell pack or module. In particular, such failures may take the form of thermal runaway or accelerating capacity fading.
Thermal management systems based on the use of active cooling (e.g., such as based on forced circulation of air, liquid or other selected cooling medium) have been proposed for use in conjunction with such battery power supply systems. Specific forms or types of active cooling include: “internal active cooling” wherein a selected cooling medium is typically circulated internally within the battery module or pack and “external active cooling” wherein a selected cooling medium is typically circulated externally to the battery module. It will be appreciated, however, that the incorporation and use of internal active cooling regimes may introduce undesired weight and/or a level of complexity in either or both power supply design and operation and such as may hinder or prevent the more widespread use of such corresponding power supply systems.
Further, the required or desired size of a battery power supply is generally dependent on the specific application thereof. Thus, certain contemplated or envisioned applications for such power supplies, such as to power electric vehicles, for example, may necessitate the use of such power supplies which have or are of significantly larger physical dimensions than those presently commonly used or available. As will be appreciated by those skilled in the art, thermal management in power supply systems can become even more critical or significant as the size of such cell, battery module, or battery pack is increased.
U.S. Pat. Nos. 6,468,689 and 6,942,944 are directed to thermal management of battery systems. There is a continuing need for improved thermal management systems and structures for battery systems.